1. Field of the Invention
The present invention relates to a digital signal processing apparatus of a communication terminal and a voice data transmission method thereof, and more particularly to a digital signal processing apparatus of a communication terminal, which performs speech coding and channel coding for detected voice data corresponding to allotted packet channels, and inserts the coded voice data into pertinent packet channels to output the inserted voice data, and a voice data transmission method thereof.
2. Description of the Related Art
Mobile telephone technology supporting wireless data packet transmission includes GPRS (General Packet Digital Radio Service), GSM (Global System for Mobile) and so forth.
GPRS can allot dynamic uplink channels in a wireless network supporting packet link for wireless data packet transmission. However, the GSM supports only a circuit-switched call processing method in channel allotment for packet transmission.
That is, the GPRS can maximize the utilization efficiency of the channels by allotting real uplink channels only in the case where there exist data to be transmitted by a terminal. However, the GSM allots channels fixed by the circuit-switched system, so that it may insure channel stability, but reduces the utilization efficiency of channels.
In general, it is believed that stream-type data, such as voice data, is preferably operated by the circuit-switched call processing method for channel allotment, however, a number of studies have been made into supporting dynamic uplink channel allotment by the GPRS in a packet network because of the two following reasons.
One reason is to avoid duplicate investment in uplink channels caused by supporting simultaneously voice data and other data besides voice data in a packet network. The other reason is to maximize channel utilization efficiency by reusing idle channel regions in a case in which a user's voice doesn't exist in a voice call. That is, it is often the case that one user of two users listens while the other user speaks during a voice call, and then, if the idle channel is reused, it will be possible to greatly increase the utilization efficiency of the channels.
In a wireless data packet transmission method having dynamically allotted uplink channels, support for a voice call has two problems as follows. First, when an overload is suddenly generated in a network, it is difficult to provide assurance of the best channel allotment, and thus it is a problem that channel allotment is not stabilized. Secondly, the other problem is that delay time—which is generated through a serial process in which channel allotment is requested by a communication terminal, channels are allotted according to the channel allotment request and communication is performed by using the allotted channels—is suitable for such a communication as web browsing but is not suitable for stream-type communication such as a voice call. That is, a voice call demands that a system's delay time for channel allotment is minimized.
FIG. 1 is a schematic view illustrating an allotment process of packet channels in a network supporting transmission of wireless data packets, such as GPRS. A network for wireless data packet transmission includes a communication terminal (hereinafter, referred to as “terminal”) 3 performing communication through allotted packet channels, a BTS (Base station Transceiver Subsystem) 5 for relaying intercommunication between the terminal 3 and an outside communication apparatus, and a PCUSN (Packet Control Unit Supporting Node) 7 allotting packet channels dynamically to the terminal.
First, the terminal 3 requests allotment of packet channels while transmitting desired data traffic information and so forth to the BTS 5 on session connection (step S1). The BTS 5 transmits data traffic information transmitted from the terminal 3 to the PCUSN 7. The PCUSN 7 allots uplink packet channels (Step S12) for terminal 3 on the basis of received data traffic information and transmits allotted information through the BTS 5 (step S14). Therefore, the terminal 3 performs communication with outside communication apparatus by using the allotted packet channels.
Meanwhile, the PCUSN 7 may use one of many kinds of periods in order to allot the number of uplink channels, and especially a coding block maybe be used as a period. That is, the PCUSN 7 continuously provides the channel number and physical information to be used at the time of the next uplink to each down-link data block.
The PCUSN 7, which controls allotment of uplink packet channels, must also provide packet channel allotment services to many different communication apparatuses requesting allotment of packet channels. Therefore, the PCUSN 7 may be suddenly overloaded when communication apparatuses simultaneously request a large amount of uplink packet channel allotment, thus it is difficult to secure the best channel allotment requested by the communication apparatuses.
Also, if the PCUSN 7 allots packet channels according to signals requesting packet channel allotment and keeps a static state with the allotted packet channels, even if there is no voice data to be transmit by a terminal 3, it is impossible to reuse the packet channels, resulting in a reduction in the utilization of the channels.
On the other hand, when the PCUSN 7 allots fewer packet channels than requested by a terminal 3, the terminal 3 cannot transmit voice data within the transmission delay time required for transmitting voice data. That is, in a situation that a great number of channels for transmission, like for data calls, is needed, the terminal 3 cannot wait for a sufficient number of channels to be allotted later on, while enduring the data's transmission delay caused from insufficiency of the allotted channel number. In this case, some voice blocks cannot help but be destroyed in order to transmit data without errors, so that there is a problem of extreme reduction of speech quality.